High vacuum pump



K. c. D. HICKMAN HIGH VACUUM PUMP -iled Aug. 9, 1938 2 Sheets-Sheet lMooofo o noun KEMVETH CDHICKMAN I NVEN'T 0R ATTORNEYS Patented Aug. 13,1940 TATE PA if HIGH VAGUUM P Application August 9, 1938, Serial l lo.223,925

8 Claims.

This invention relates to improved apparatus for producing high vacuaand in. particular relates to improved condensation or diffusion pumps.

In my U. S. Patent 2,080,421 I have described improved condensationpumps adapted to employ an organic working fluid. These pumps areadapted to fractionate the organic pump fluid during use and deliver thevapors of the various fractions to appropriate jets in the pump. Thepumps described in 'this patent are a big improvement over pumps of theprior art. However, even with the fractionating features, these pumps donot give pressure reductions corresponding to theory. This has beenfound to be particularly true in connection with vertical fractionatingpumps wherein a plurality of boiler compartments are formed in the baseby concentric tubes which deliver vapors to, appropriately located jetsat the upper ends of the concentric tubes.

An object of my invention is to provide improved fractionatingcondensation or diffusion pumps. A further object is to provide improvedfractionating condensation pumps of the vertical concentric tube type. Astill further object is to provide fractionating condensation pumpswhich will yield pressure reductions corresponding to theory. A stillfurther object is to provide condensation pumps which will yieldpressure reductions approximately as low as the vapor pressure of thelowest vapor pressure constituents of the pump fluid which can bevaporized without decomposition. Other objects will appear hereinafter.

These and other objects are accomplished by my invention which ingeneral comprises arranging the boiler compartments or the vaporconduits between the boiler compartments and the jetnozzles so that thelowest vapor pressure components of the pump fluid, which cannot bevaporized without decomposition, are delivered to a jet nozzle at leastonce removed from the highest vacuum jet nozzle so that the next lowestvapor pressure components, which can be vaporized without appreciabledecomposition, are delivered to the highest vacuum jet.

The reason why theoretical pressure reductions were not obtained in theearlier constructions has been found to be due to the fact that thelowest vapor pressure constituents cannot be vaporized without at leastpartial thermal decomposition. Heretofore, the vapors from the lowestvapor pressure constituents were delivered to the highest vacuum jet.Therefore, these volatile decomposition products were released at apoint in the pump where they could do most harm. ,By bypassing theseharmful constituents to a low vacuum or intermediate vacuum jet they areprevented from exerting their harmful action and are, in fact, caused toperform useful pumping 5 action.

In the following description I have given numerous examples of thepreferred embodiments of my invention. However, it is to be understoodthat these are given for the purpose of illustration and not aslimitations thereof. 1

In the accompanying drawings:

Fig. l is an elevation in section of a vertical concentric pumpembodying the principles of my invention wherein vapors from the lowestvapor s pressure constituents are by-passed to the lowest vacuum jet;

Fig. 2 is a horizontal section on line- 2--2 of Fig. 1;

Fig. 3 is an elevation in section of a vertical concentric pump whereinthe lowest vapor pressure constituents of the pump liquid are bypassedfrom the boiler supplying the high vacuum jet to the boiler supplyingvapors to a jet operating against an intermediate vacuum;

Fig. 4 is a horizontal section on line Qt of Fig. 3;

Fig. 5 is a sectional elevation of a horizontal fractionating pumpwherein the vapors are bypassed;

Fig. 6 is a vertical section on line 66 of Fig. 5 and is shown on aslightly reduced scale;

Fig. 7 illustrates in sectional elevation a modified horizontalfractionating pump wherein the lowest vapor pressure constituents areby-passed in liquid form from the lowest vapor pressure boiler to anintermediate boiler supplying vapors to the next lowest vacuum jet;

Fig. 8 is a vertical section on line t8 of Fig. 7.

Referring to Fig. 1, numeral 2 designates a cylindrical pump casing, thebase of which is closed by an integral plate t, the center of which isconnected to ,a withdrawal conduit 6. The top of the casing 2 isprovided with a flange 8 which facilitates connection to the systemwhich is to be evacuated. The upper end, therefore, represents the highvacuum or intake side of the pump.

The low vacuum side, or exhaust side of the pump is indicated by conduitIll which connects to the backing pump (not shown). Numerals l2, l4 andI6 designate approximately concentric cylinders, the base ofeach ofwhich is in close, and preferably liquid-tight contact with the baseplate d. Concentric cylinder l2 is provided with a collar I8 atits basewhich extends into close proximity to the inner wall of pump casing 2.Cylinder I2 is truncated at the top and the truncated portion isextended to, and integral with, concentric cylinder I4. Concentriccylinder I4 is similarly truncated at I9. Cylinder I6 is truncated at 20as illustrated in order to form a chimney for vapors passing to thehighest vacuum jet.

Numerals 22, 24 and 26 designate annular jet lips integral with theperiphery of cylinders I2, I4 and I6 respectively, so as to form low,intermediate and high vacuum jet nozzles. Numerals 28, 30 and 32designate openings through which vapors issue into the jet nozzles fromthe spaces between the concentric cylinders. Numeral 34 designates theannular boiler formed at the base by concentric cylinders I2 and I4which supplies working vapor to jet nozzle 22. Numeral 35 designates anannular boiler which Sup lies working vapor to jet nozzle 24. Numeral 38designates an annular boiler which supplies working vapor to jet nozzle26. Numeral 40 designates a conduit, the lower end of which is integralwith and penetrates through concentric cylinders I4 and I6. This conduitcovers a circular central portion 42 which serves as a boiler for thelowest vapor pressure constituents.

Numeral 44 designates a collar which supports the entire pump assemblyand which provides a circular space, closed by plate 46 within which ismounted a plurality of heating units as illustrated. Each of theseheating units is adapted to heat the boiler compartments 34, 36, 38 and42 to separate and independent temperatures.

Referring particularly to Fig. 2, numeral 41 designates an opening inthe base of concentric cylinder I2. This opening is sufiiciently lowthat its upper portion is well covered by the pump liquid in the boiler.Numeral (l8 designates a similar opening in the base of cylinder I5.Numeral 50 designates a small opening in the base of concentric cylinderI6. Numeral 52 designates a similar opening in the base of cylinder 40.

Referring to Figs. 3 and 4, concentric cylinders I2, I4 and I6 aremounted within the main cylindrical casing as described in connectionwith Figs. 1 and 2. These cylinders are in liquidtight contact with thebase 0 and cylinders I2 and I4 are truncated as previously described.However, cylinder I6 extends, without constriction directly to the highvacuum jet 26. Numeral 60 designates a conduit integral with concentriccylinders 4 and I6 which provides a passageway for the flow of pumpliquid from boiler compartment 34 into boiler compartment 38. A bafile62 in 1 he shape of an annular ring is located in the boiler 38 and issplit at 64 as indicated. Passage 60 is sufficiently low that its topportion is well covered by pump liquid. A similar passageway 66 connectsthe inside of bafile 62 with boiler compartment 36. An electricalheating element 68 is mounted in the base. It is not shown as beingcontrollable so as to heat each boiler compartment to an independenttemperature. However, the amount of heat supplied to each boilercompartment can be regulated by varying the proportion of heating unitplaced under each compartment.

Referring to Figs. 5 and 6, numeral 00 designates a cylindrical pumpcasing which is adapted to be connected at the high vacuum end by flange82 to the chamber to be exhausted, and at the low vacuum end by conduit86 to a backing pump (not shown). The low vacuum end of is closed by aplate integral with conduit 80. The base of cylinder 80 in the vicinityof the low vacuum end is cut away and the extended walls.85 and 81,closed by a base plate 88 so as to form a recessed pump fluid boiler. Asimilarly shaped cylinder 90 is located within the main casing 80 andmore or less concentric therewith. The portion of this cylinder adjacentthe low vacuum end of the pump is cut away and provided with anextension corresponding to that of the pump liquid boiler. The end ofthe cylinder 90 is closed by a plate 92 which is integral with a conduit93 which extends slightly into conduit 84 as illustrated. Plate 92extends to the base plate 88 of the boiler. A similarly shaped plate 94located inside the cylinder 90 .extends from the top inside wall of thecylinder to the base plate 88. Plate 96 is similarly shaped and likewiseextends to the base plate 88. Plate 98 is integral with the lower wallof cylinder 90 and extends to the base plate 88 of the boiler. Two bentplates I00 and I02 integral with the lower wall of the cylinder 90,extend transversely to plates 92, 94, 96 and 98 and are integraltherewith. They serve to segregate the pump liquid boiler into aplurality of compartments, A, B and C. Cylinder 90 is truncated at 99and the truncated portion is extended to, and becomes integral withconduit I04. Jet nozzle I06 is mounted at the high vacuum end of conduitI04. Jet nozzle I08 is similarly located at the end of cylinder 90.Holes I09 and H0 provide a passageway for Working vapors to issue intojets I06 and I08 respectively. Numeral II2 designates a series ofstaggered bafiles which are located in the various boiler compartments.They cause the pump fluid to flow in a tortuous path or at a slow ratein passing through the boiler compartments.

Numeral H4 designates a semi-circular opening in the base of plate 98.It is sufficiently small that it is well covered by pump fluid. Theseopenings are two in number. Numerals H6, H8 and I20 designate similaropenings in the base of plates 92, 94 and 96 respectively. Numeral II5designates a conduit which extends along the base of the boiler throughopenings in the various baffle and partition plates. These openings arepreferably small so that a tight fit results. Conduit H5 is bent upwardat II! and terminates at the bottom central portion of the casing 80.The other end of the conduit terminates at the low pressure end of theboiler.

Numeral I2I designates a series of fractionating rings integral with thewall of conduit 84. Conduit I23 connects the space between the last tworings I2I with the low pressure portion of the boiler. Numeral I22designates a cooling coil integral with the external wall of the pumpcasing. Cooling fluid is introduced at I24 and with drawn at I26.Numeral I28 designates a sightglass whereby the level of the pump fluidcan be readily determined.

Referring to Figs. '7 and 8, numeral I50 designates an approximatelycylindrical pump casing, the high vacuum end of which is provided with aflange I52 which is adapted to be connected to the chamber to beevacuated and the low vacuum end of which is shown is connected to aconduit I54 which is in turn connected to a backing pump (not shown).The base of pump casing I50 is cut out at a point beginning at thecentral portion to the low vacuum end. The walls of the base near thecut out area are extended to form an elongated reservoir having wallsI58 and I5? and base I58. A cylindrical element IE0 is located insidethe pump casing sponding to the location of the reservoir in the and hasits base cut away in a position correbase of casing I50. Internalcylindrical element I60 is divided into a plurality of compartments D,E, F and G by partitions I62, I66, I64 and I65 which extend to the baseplate I58 of the titions I62 and I63 are provided with a plurality I I02and I'I4 which permit pump liquid to of small notches I68 which are wellbelow the level of the pump liquid in the boiler. Partition I64 extendsentirely to the base plate I58 and makes substantially liquid-tightcontact therewith. Partition I 65 is provided at its base with aplurality of notches H0. The walls of cylindrical element I60 areextended to the base of the boiler at I12 and H4 which are at asuflicient distance from walls I56 and I61 to just permit pump liquid toflow therebetween. Numeral I16 designates a plurality of minute notches,in walls flow back into the boiler compartments.

Referring particularly to Fig. 8, it will be noticed that partitions I64and I65 do not extend to wall I I4. They are shortened, as shown, andare connected by a plate I16 soas to form a passageway I60 from theboiler of compartment E directly into the boiler of compartment G.

Reference numerals I62, I64, I66 and I66 designate jet nozzles whichcommunicate with compartments D, E, F, and G by openings I90, I92, I64and throat I96, respectively. Numeral 200 designates a bafileconstructed of a metal conduit wound in the form ofa helix. Coolingfluid is supplied to this baiile by introduction at 202 and withdrawalat 204.

, In operating the apparatus illustrated in Fig. 1, an organic pumpfluid is introduced into the pump. It should be filled to a heightsuflicient to at least cover the openings 46, 66 and 52. Flange'6 isconnected to the system to be evacuated and conduit I0 is connected to abacking pump in the usual manner. Conduit 6 is closed or is connected toa small air-tight sump. The base of the pump is then heated by theelectrical heating element. It is best that the temperature uniformlyincrease toward the center of the pump. Vapor produced in boiler section64 rises in the annular space between concentric tubes I2 and I4 andpasses through holes 28 and issues from jet nozzle 22. The jet entrainsgases in known manner which are removed by the backing pump throughconduit III. The jet vapors condense on the walls of casing 2, flow bygravity into the space between I6 and 2 and arrive back into the boilercompartment 24 from which they were derived by way of opening 41. Theunvaporized liquid in compartment 64 flows in a circular path to opening46 and into boiler compartment 86. When the liquid arrives incompartment 66 it has traveled in a tortuous path through boiler 34 andhas, therefore, been thoroughly deprived of high vapor pressureconstituents before passing through opening 46.

In compartment 66 the next lowest, below the high vapor pressureconstituents are vaporized and pass upwards between concentric cylindersI4 and I6. These vapors issue through openings 30 and pass out throughjet nozzle 24. Vapors are condensed on the inside wall of easing 2 andthe condensed liquid flows back into boiler compartment 24. The pumpfluid which .is not vaporized in compartment 26 passes ima circular ortortuous path to passage 60 and into boiler compartment 68. Here thenext lowest, to the lowest 'vapor pressure components are vaporized andrise and issue through openings 32 and pass from jet nozzle 26., Jet 26is the highest vacuum jet and it is desirable that it be supplied withthe best portion of the pump fluid vapors. Vapors issuing from jet 26are condensed on the walls 02 casing 2 and flow by gravity back intoboiler Pump fluid which is not vaporized in boiler compartment 38 thenflows through opening 62 into boiler compartment 42. These pump fluidconstituents are the lowest vapor pressure components. However, theyhave such a low vapor pressure thatthey cannot beefliciently vaporizedwithout some thermal decomposition. The vapors derived therefrom are,therefore, not suitable for delivery to the high vacuum jet 26. Thesevapors rise through L-shaped conduit 40 and pass into the annular spacebetween concentric tubes I2 and I6 and eventually pass ou through jet22.

It is apparent that eflicient fractionation of the pump fluid takesplace in the operation of this apparatus. The pump fluid is segregatedinto components of gradually increasing vapor pressure as in priorconstructions but the lowest vapor pressure component is segregated andis not permitted to be vaporized and delivered to the highest vacuumjet. The harmful effects of its decomposition products are therebyavoided. A further feature of novelty which also adds to the eflicientoperation of the vertical concentric fractionating pump is illustratedin Figs. 1 and 2. 7

It will be noted that the boiler area in boiler compartment 36 isincreased so that it is approximately the same as the boiler areas ineach of, the other compartments. This permits effective vaporization ofpump fluid in ample quantities for operation of the high vacuum jetwithout overheating.

The feature of causing the pump fluid to pass in a tortuous path througheach boiler compartment is also of decided advantage and can be used infractionating pumps of all types. If the pump fluid is permitted to flowtoo quickly from one compartment to another it is not efiicientlystripped of its lighter constituentsand these will be vaporized at apoint where they may adversely affect the pumping action. By causingliquid to pass in a tortuous, path removal of. all volatile constituentsbefore it reaches the next boiler compartment is assured Duringoperation of the apparatus illustrated in Figs. 3 and 4, fractionationand the action of the jet is similar to that of the apparatusillustrated in Fig. 1. However, the pump liquid in boiler 64 flowsdirectly into boiler compartment 38 through conduit 60. The highestvapor pressure constituents are, therefore, vaporized in compartment 34and issue through jet 22. The intermediate vapor pressure constituentsare vaporized in boiler compartment 66 and in the area within ring 62.These vapors rise and issue through high vacuum jet 26. The lowest vaporpressure constituents remain unvaporized and pass through passageway 66into intermediate boiler compartment 66. Here the lowest vapor pressurecomponents which undergo more or less decomposition are vaporized andthe vapors delivered to jet 24 which operates against a lower v vacuum.

In both concentric pumps illustrated in Figs. 1

mulate. These can intermittently be withdrawn by suitably located.conduits such as conduit 8.

In operating the apparatus illustrated in Figs. 5 and 6, pump fluid isintroduced into the boiler compartment. The pump fluid is indicated at Iand is shown as it would be retained by the boiler during operation ofthe pump. It will be noted that the pump casing 80 and the base oi theboiler 88 slant upwardly toward the high vacuum end. This is to causethe pump liquid to flow back into the boiler compartments. Flange 82 isconnected to the chamber to be evacuated and conduit 84 is connected toany suitable backing pump. The boiler containing the pump fluid isheated in any suitable manner, such as by gas. The highest vaporpressure pump fluid constituents vaporize and pass into compartment Aand thence through jet nozzle 93. The jet of vapors passes into conduit84 where it is condensed and entrained gases removed by the backing pumpconnected thereto. The condensed pump liquid flows back overfractionating sure so that the pump fluid is caused to flow more or lessup-hill into compartment B. In compartment B the intermediate fractionrepresenting the most useful components of the pump fluid is vaporizedand passes into conduit I04 and thence to jet I06. Vapors from this jetcondense on the cooled walls of 80 and flow to the base and into conduitI I5. They then flow through conduit H5 to the lowest portion of theboiler as indicated at I21. The lowest vapor pressure constituents arenot vaporized in compartment B, but flow into compartment C. vaporpressure, decomposable substances are vaporized and issue through theintermediate jet I08. Vapors from this jet condense on the walls ofcasing 80 and flow by gravity back into conduit H5 and eventually returnto compartment I21.

The staggered baflies H2 in each of the boiler compartments cause thepump fluid to pass in a tortuous path as explained above. Sight-glassI28 permits accurate determination of the level of the pump fluid in theboiler.

It will be noted that in the apparatus illustrated in Figs. 1, 3 and 5the conduit conveying vapors to the highest vacuum jet is more or lesscompletely surrounded by heated vapors which pass to an intermediatejet. This eflectively prevents the low vapor pressure constituentspassing to the highest vacuum jet from condensing before they reach thejet. The eificiency of the jet is thereby increased.

In operating the apparatus illustrated in Figs. '7 and 8 conduit I54 isconnected to a backing pump and flange I52 is connected to a receptacleto be evacuated. The boiler compartments are filled with an appropriatepump fluid to a level well above the top of openings H0 and I16, etc. Inthe boiler of compartment D, the highest vapor pressure constituents arevaporized, rise through compartment D, pass through openings I90 andissue from jet I82. The vapors condense on the wall of easing I50, flowby gravity into the space between wall I56 and wall H2 and thencethrough Here the low.

openings I16 back into the boiler compartment. Liquid which is notvaporized in compartment D then flows through openings I68 in partitionI63 and are vaporized in compartment E and issue from jet nozzle I84.The remaining unvaporized liquid then by-passes compartment F throughpassage I80 and directly flows into the boiler 01 compartment G. Herethe most useful vapor pressure constituents for the high vacuum Jetnozzle I88 are vaporized and pass through that jet. Unvaporized residuethen passes backwards through openings H0 in the base of partition I65and into the boiler of compartment 1. Here non-volatile residuesaccumulate and low vapor pressure constituents which cannot be vaporizedwithout decomposition are vaporized and delivered to jet nozzle 88 wherethey perform useful pumping action. Vapors from each of the jets arereturned to the boiler compartments in the same manner described inconnection with compartment D.

Any vapors which might diffuse backwards into the zone under evacuationare condensed upon baflle 200. This bafiie may be constructed in otherways well known in the art but the shape shown has been found to havehigh efficiency. A bafile should present as little resistance to theflow of gases into the pump as is possible.

The apparatus illustrated in Figs. 7 and 8 may be provided with atilting device so that the level of the pump fluid in the variousboilers may be appropriately controlled. The base of the boiler maylikewise be slanted as illustrated in connection with Fig. 5.

The apparatus illustrated may be constructed of any suitable materials.Any of the apparatus illustrated may be constructed entirely of metal.The apparatus of Figs. 1 and 3 can be conveniently constructed partly ofglass so that the operation of the pump can be observed. The jet nozzlescan be conveniently spun from aluminum and the standpipes and otherparts can also be constructed of this metal, although steel, iron,copper, etc., may be used.

This application is a continuation in part of my U. 8. application143,305 filed May 18, 1937. now Patent 2,153,189, granted April 4, 1939.

What I claim is:

1. In a multi-stage fractionating vacuum pump provided with a pluralityof Jet nozzles adapted to operate in series and a plurality of boilercompartments adapted in operation to arrange the low vapor pressurecomponents of the pump fluid so that they exert their pumping actiontoward the high vacuum side and the high vapor pressure componentstoward the low vacuum side, the improvement which comprises a vaporpassage conduit connecting the boiler compartment containing the lowestvapor pressure components to a jet nozzle intermediate the lowest andhighest vacuum jet nozzles, and a vapor passage conduit connecting theboiler compartment containing the next lowest to the lowest vaporpressure components to the highest vacuum jet, whereby the lowest vaporpressure components of the pump fluid are not vaporized and passed tothe highest vacuum jet where they would do harm but instead are utilizedin a lower' vacuum jet where they do not exert harmful effects.

2. In a multi-stage fractionating vacuum pump provided with a pluralityof jet nozzles adapted to operate in series and a plurality of boilercompartments adapted in operation to arrange the low vapor pressurecomponents of the pump fluid so that they exert their pumping actiontoward upper end with one of said nozzles and. termithe high vacuum,side and the high vapor pressure components toward the low vacuum side.the improvement which comprises a restricted pump liquid passagedirectly connecting the boiler compartment supplying working vapors tothe high vacuum jet with the boiler compartment supplying vapors to ajet at least once removed from the high vacuum-jet, and a restrictedpump liquid passage between the boiler compartment supplying the highvacuum jet with working vapors, and the boiler compartment supplyingworking vapors to the jet next to the high vacuum jet whereby the lowestvapor pressure compo-- nents of the pump fluid are not vaporized andpassed to the highest vacuum jet where theywould do harm, but insteadare utilized in a lower vacuum jet where they do not exert harmfuleffects.

3. In a multi-stage fractionating vacuum pump provided with a pluralityof jet nozzles adapted to operate inseries and a plurality of boilercompartments adapted in operation to arrange the low vapor pressurecomponents of the pump fluid so that they exert their pumping actiontoward the high vacuum side and the high vapor pressure componentstoward the low vacuum side the improvement which comprisesa vaporpassage conduit "connecting the boiler compartment containing the lowestvapor pressure components to a jet nozzle intermediate the lowest andhighest vacuum jet nozzle and a vapor passage conduit connecting theboiler compartment containing the next lowest vapor pressure componentswith the highest vacuum jet whereby the lowest vapor pressure componentsof the pump fluid are not vaporized and passed to the highest vacuum jetwhere they would do harm, but instead are utilized in a lower vacuum jetwhere they do not I exert harmi'ul efl'ects.

4. In a multi stage iractionating vacuum pump 1 provided with aplurality of jet nozzles adapted to operate in series and a plurality ofboiler compartments adapted in operation to arran e the low vaporpressure components of the pump fluid so that they exert their pumpingaction toward the high vacuum side and the high vapor pressurecomponents toward the low vacuum side the improvement which comprises avapor passage conduit connecting the boiler-compartment containing thelowest vapor pressure components to a jet nozzle at least .once removedfrom the h ghest vacuum jet nozzle, and a vapor passage conduitconnecting the boiler compartment containing the next lowest vaporpressure component with the highest vacuum jet whereby the lowest vaporpressure components of the pump fluid are not vaporized and passed tothe highest vacuum jet where they would do harm, but

instead are utilized in a lower vacuum jet where they do not exertharmful eflects.

5. A multi-stage fractionatiug vacuum pump adapted in operation toarrange the components of the pump fluid so that the low vapor pressurecomponents exert their pumping action toward the high vacuum side andthe high vapor pressure components toward the low vacuum side 01 thepump, comprising in combination a tubular chamber with an outlet portnear the lower end and an inletport above the outlet port, means to heatthe base of the tubular chamber, a plurality of nozzles in series fromthe high vacuum to the low vacuum side mounted one above the otherbetween said ports and directed toward the outlet port, a plurality ofapproximately concentric conduits each communicating at the hating atthe bottom of the chamber to form a plurality of boiler compartments inthe chamber below the outlet port, restricted passages in sequencebetween adjoining boiler compartments, except those supplying vapors tothe two highest vacuum Jets, a, restricted pump liquid passage betweenthe boiler compartment supplying working vapors to the high vacuum jetand the boiler compartment supplying vapors to a jet at least onceremoved from the highest vacuum jet and a restricted pump liquid passagefrom the boiler compartment supplying the high vacuum jet with workingvapors to the boiler compartment supplying working vapors to the jetnext iii the series to the high vacuum jet whereby the lowest vaporpressure components of the pump fluid are not vaporized and passed tothe highest vacuum jet where they would do harm, but instead areutilized in a lower vacuum jet where they do not exert harmful effects.

6. A multi-stage fractionating vacuum pump adapted in operation toarrange the components of the pump fluid so that the low vapor pressurecomponents exert their pumping action toward the high vacuum side andthe high vapor pressure components toward the low vacuum side of thepump, comprising in combination a tubular chamber with an outlet portnear the lower end and an inlet port above the outlet port, means toheat the base 01' the tubular chamber, a plusure components, to a jetnozzle at least once removed from the highest vacuum jet nozzle and avapor passage from the boiler compartment containing the next lowest tothe lowest vapor pressure components to the highest vacuum jet wherebythe lowest vapor pressure components of the pump fluid are not vaporizedand passed to the highest vacuum jet where they would do harm, butinstead are utilized in a lower vacuum Jet where they do not exertharmful efl'ects.

'I. In a multi-stage tractionating vacuum pump provided with a pluralityof jet nozzles arranged in horizontal series and adapted to operate inseries and a horizontal boiler divided into a plurality of compartmentsby approximately vertical partitions and adapted in operation to ar- 7range the low vapor pressure components of the pump fluid so that theyexert their pumping action toward the high vacuum side and the highvapor pressure components toward the low vacuum side, the improvementwhich comprises a vapor passage conduit connecting the boiler commentcontaining the next lowest to the lowest vapor pressure component withthe highest vacuum jet whereby the lowest vapor pressure components oithe pump fluid are not vaporized and passed to the highest vacuum jetwhere they would do harm, but instead are utilized in a lower vacuum,jet where they do not exert harmiul eflects.

8. A multi-stage fractionating vacuum pump adapted in operation toarrange the components of the pump fluid so that the low vapor pressurecomponents exert their pumping action toward the high vacuum side andthe high vapor pressure components toward the low vacuum side of thepump, comprising in combination a tubular chamber with an outlet portnear the lower end and an inlet port above the outlet port, means toheat the base of the tubular chamber, a plurality 01' nozzles mountedone above the other between said ports and directed toward the outletport, and a plurality of approximately concentric conduits eachcommunicating on the upper end with. one of said nozzles and terminatingat the bottom of the chamber to form a plurality of boiler compartmentsin the chamber below the outlet port. the concentric conduits being ofsuch diameter that approximately the same area of the bottom of thechamber is enclosed between each pair of 10 conduits.

KENNETH C. D. HICKMAN.

